This invention relates to equipment which may be used amongst other purposes for controlling the production flow from subsea oilwells. More specifically it relates to couplers which may be used in pressure containing conduits extending between a tubing hanger and a horizontal Christmas tree.
In subsea oilwells there is a requirement to provide a hydraulic communication line to a surface controlled subsurface safety valve (SCSSV) located within the well for controlling production flow. A second line may be provided to the SCSSV to allow flushing and circulation/replacement of the control fluid. Additional pressure lines may be present for chemical injection or control or monitoring of other downhole equipment. To cater for maximum variation in chemical and fluid composition in the lines it is desirable that metal to metal primary seals should be used.
With a horizontal Christmas tree system, the pressure lines must come from within the tubing hanger and completion equipment out through the Christmas tree. Pressure line connections must be made up after or during installation of the tubing hanger which occurs after the Christmas tree has been installed. There are various known arrangements for providing such connections. In a first arrangement, a circumferential sealed pressure gallery extends between ports in the tubing hanger and Christmas tree. This design is limited by the space required which restricts the number of pressure lines and the facility for backup seals. A second arrangement has angled couplers upstanding from the tubing hanger and/or Christmas tree which are made up automatically as the tubing hanger is installed (i.e. tubing hanger weight set). This design may require complex machining internal to the Christmas tree and tubing hanger. A third arrangement is a single pressure line coupler movable in and out of mating engagement with the tubing hanger by a manual actuator mechanism. The problems in this design are in providing a dynamic seal between the movable coupler and stationary pressure line to accommodate the actuator stroke. This effectively precludes the use of metal to metal seals throughout the coupler. The actuator mechanism must also be made highly reliable as the coupler has to be retracted to allow retrieval of the tubing hanger. Failure of the actuator mechanism with the coupler extended will lead to severe problems in removing the tubing hanger from the Christmas tree.